Mass spectrometry, including, FAB-MS, FAB-CAD-MS/MS, MALDI-MS and ESI-MS has continued to provide structural information for the Macromolecular Structure Facility, particularly in cases where traditional Edman degradation chemistry is not applicable, or does not provide complete structural information. Molecular weights have been obtained for N-terminal blocked peptides of known sequence and for phosphorylated peptides. Synthetic peptides are also now routinely characterized by mass spectrometry prior to release for biological studies. MALDI-MS and peptide mass mapping have also been used to characterize recombinant proteins.